Issue #3343755 by kim.pepper, catch, smustgrave, longwave: Simplify TimeZoneFormHelper

core/lib/Drupal/Core/Datetime/TimeZoneFormHelper.php

.../Field/Plugin/Field/FieldFormatter/TimestampFormatter.php

core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php

...src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php

core/modules/system/src/Form/RegionalForm.php

core/modules/system/system.module

...tem/tests/src/Kernel/System/SystemFunctionsLegacyTest.php

core/modules/user/src/AccountForm.php

core/modules/views/src/Plugin/views/field/Date.php

...sts/Drupal/Tests/Core/Datetime/TimeZoneFormHelperTest.php